Process of reducing generation of benzo[a]pyrene during smoking

ABSTRACT

A process for manufacturing a smoking article having reduced generation of benzo[a]pyrene during smoking thereof comprises preparing a treated tobacco by contacting a tobacco material with an extraction solvent consisting essentially of methanol, ethanol, 1-propanol or 2-propanol; and incorporating the treated tobacco in a smoking article.

This application claims the benefit of U.S. Provisional Application No. 60/631,984, filed Dec. 1, 2004, which is incorporated herein by reference in its entirety.

SUMMARY

A process for manufacturing a smoking article having reduced generation of benzo[a]pyrene (B[a]P) during smoking thereof comprises preparing a treated tobacco by contacting a tobacco material with an extraction solvent consisting essentially of methanol, ethanol, 1-propanol or 2-propanol; and incorporating the treated tobacco in a smoking article.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 depicts B[a]P yields from the 600° C. pyrolysis in Helium of solvent extracted bright tobacco (120 ml/min flow rate, 600° C./min heating rate, 10 min).

FIG. 2 depicts the effect of proline (0.4% w/w) and lipids on the yield of B[a]P from the 600° C. pyrolysis of a carbohydrate+lignin mixture. The lipid mixture consists of oleic acid (1 mg), linoleic acid (2 mg), linolenic acid (3.5 mg), stigmasterol (0.8 mg, chlorogenic acid (8 mg) and solanesol (15 mg) dissolved in methanol.

DETAILED DESCRIPTION

The formation of polycyclic aromatic hydrocarbons (PAHs) from tobacco has been extensively studied over the past four decades. Benzo[a]pyrene (B[a]P), a 5-ring PAH, has received much attention. Of the many individual component classes in tobacco (alkaloids, reducing sugars, cellulosic materials, long-chain hydrocarbon waxes, amino acids, proteins, etc.), lipophilic tobacco components such as phytosterols, saturated aliphatic hydrocarbons, and terpenoid compounds were believed to be the major precursors of PAHs formed from a burning cigarette. Most of the data put forth in the literature to support the proposed precursor pools was obtained from pyrolysis experiments carried out on tobacco, selective tobacco extracts, and individual tobacco components at temperatures >700° C. and at gas phase residence times on the order of seconds to 10's of seconds. The recently reported formation of quantifiable amounts of 2 to 5 ring PAHs at pyrolysis temperatures below 600° C. in μg/g quantities from tobacco and carbohydrate samples such as cellulose, glucose, and sucrose highlights a low temperature mechanism for PAH formation.

A number of solvent extracted tobaccos and individual tobacco components such as sterols, long-chain hydrocarbons, fatty acids, carbohydrates and polyphenols have been pyrolyzed at 600° C. in an effort to identify low temperature B[a]P precursors. The yield of B[a]P obtained per gram of sample pyrolyzed has been normalized to the amount of each component present in tobacco. The B[a]P yield from a mixture of selected tobacco lipophilic and cell wall components has also been investigated.

The pyrolysis setup used was described in McGrath, T. E. et al., J. Anal. Appl. Pyrol., 66 (2003) 51-70. The experimental setup consisted of a 2.5 cm i.d. quartz tube placed inside a 30 cm long heated Carbolite furnace having an isothermal length of ca. 7 cm at a temperature of 600° C. Helium was used as the carrier gas at a flow rate of 120 cm³/min. The residence time of gas phase pyrolysis products in the isothermal section of the reactor was calculated to be approximately 4 s at a furnace temperature of 600° C. A fiber-glass filter placed in a housing assembly immediately at the end of the quartz tube on the exit side of the furnace was used to collect the product tar condensate. The temperature of the sample in the heated quartz tube was measured using a chromel/alumel (K type) thermocouple. The thermocouple was also used to transport the ceramic boat containing the samples to and from the heated isothermal region of the quartz tube.

Tobacco Samples—Bright (flue cured) lamina and bright lamina extracted with hexane, ethyl acetate, methanol and water were ground (10 to 150 μm particle size) prior to pyrolysis. The hexane and ethyl acetate and methanol extracted samples were prepared using a Soxhlet extraction setup. The water extracted sample was prepared by extracting a sample of bright lamina packed in a column with a continuous stream of deionized water at room temperature. Exhaustive extraction processes in hexane, ethyl acetate, methanol and water lead to about a 4, 16, 40 and 50% reduction in sample weight, respectively.

Oleic acid (99+%), linoleic acid (99%), stigmasterol (93%) and cholesterol (99+%) were purchased from Aldrich. Linolenic acid (90%, remainder linoleic acid) and D(+)-proline (99+%) were purchased from Acros. Chlorogenic acid (95+%) and solanesol (90+% from tobacco leaves) were obtained from Sigma. A mixture of: oleic acid (1 mg/g), linoleic acid (2 mg/g), linolenic acid (3.5 mg/g), stigmasterol (0.8 mg/g), chlorogenic acid (8 mg/g) and solanesol (15 mg/g) was prepared in methanol and added to a mixture of carbohydrates and lignin.

Avicel cellulose, xylan from birch wood, pectin from citrus fruits, and hydrolytic lignin (Sigma-Aldrich) were used as model tobacco cell wall components. The Avicel cellulose sample was obtained from FCI and is a microcrystalline purified and depolymerized alpha-cellulose derived from fibrous plants (Avicel PH-102). It has an ash content of less than 0.007%. The birchwood xylan (>95% xylose) sample was obtained from Fluka. The pectin sample was obtained from Sigma and has a galacturonic and methoxy content of 81% and 8.6%, respectively. D-glucose was used as a model tobacco sugar. The D-glucose sample was obtained from Acros and is 99+% reagent grade.

A mixture of cellulose, hemicellulose, pectin, glucose, and lignin was made up with the following component ratios of 1:1:1: 1:0.3, respectively. The resulting mixture is denoted as Carbo-Lig Mix throughout the rest of the text. The major cation present in the pectin, hemicellulose and lignin samples, as determined by ICP-MS, was sodium. The samples also contained smaller amounts of Calcium.

A sample of tobacco or model tobacco compound to be pyrolyzed was placed in a ceramic boat that initially rested in an unheated section of the quartz tube outside of the heated furnace. A tar trap assembly was placed on the exit side of the furnace. After the furnace had reached the desired set temperature, for example, 600° C., the sample was pushed to the isothermal region in the furnace and pyrolyzed for a total of 10 minutes. At the end of the pyrolysis experiment, the boat was pulled back to the unheated section of the quartz tube and the remaining solid residue was allowed to cool to room temperature. The fiber-glass filter was removed, placed in an amber screw capped vial, and the washings from the pad housing assembly walls was added to the vial. A total solvent level of 5 mL of methanol was used and the vial was left to stir overnight on a shaker. At the end of each run, the quartz tube was cleaned in air at a temperature of 650° C.

The tar fractions collected were analyzed by GC-MS using an Agilent 6890 GC equipped with an Agilent 5973 quadrupole MSD analyzer operating in the single ion mode (SIM). The yield of B[a]P was calculated using a calibration curve obtained from the analysis of standard solutions of B[a]P ranging from 10 to 1000 ng/ml. The yield of B[a]P reported is the average of 3 experimental runs (n=3).

A variety of solvents with polarities ranging from non-polar to very polar were used to extract the bright tobacco lamina sample and the yields of B[a]P formed at 600° C. in Helium from the resulting extracted lamina are given in FIG. 1.

Extraction of bright tobacco lamina with either hexane or ethyl acetate (EtOAc) did not significantly affect the yield B[a]P formed compared to an unextracted control. The result suggests that non-polar tobacco components such as long-chain hydrocarbons and fatty acids which are readily removed by these solvents are not significant low temperature B[a]P precursors in tobacco. The methanol (MeOH) extracted sample gave a 35% reduction in the yield of B[a]P suggesting that a potential low temperature B[a]P precursor (or precursors) have been removed by this solvent. B[a]P reductions can also be obtained by extracting the tobacco with ethanol, 1-propanol or 2-propanol. For example, extraction of a flue-cured tobacco with ethanol gave a 60% reduction in B[a]P. In contrast, the water extracted sample gave a 107% increase in B[a]P. Extraction with water removes alkaloids, amino acids, pectin, sugars, organic acids, and phenolics from the original lamina. The water extraction process appears to remove non-PAH-forming low temperature precursors but concentrates instead (on a per unit weight basis) PAH forming precursors.

The yields of B[a]P obtained from the pyrolysis of 11 individual components at 600° C. in Helium for a total heating time of 10 min are give in Table 1. Stigmasterol, cellulose, hemicellulose, glucose and lignin gave the highest yields of B[a]P on a ng/g basis. The formation of B[a]P from the pyrolysis of fatty acids appears to increase with the number of double bonds in the structure, i.e. oleic<linoleic<linolenic acid. Although stigmasterol and the fatty acids formed B[a]P at 600° C., when the yields of B[a]P are normalized to the amount of each component in tobacco, cellulose, hemicellulose, glucose and lignin contributed significantly to B[a]P yields. TABLE 1 600° C. Pyrolysis B[a]P Yields for Tobacco Components B[a]P Yields ^(a)Norm. Tobacco at 600° C. B[a]P Yield Component (ng/g) (ng/g) Sterols Stigmasterol^(b)(˜0.8 mg/g) 1200  0.9 Isoprenoid Solanesol (20-40 mg/g) ND 0 Fatty Acids Oleic acid (˜1 mg/g)  80 0.08 Linoleic acid (˜2 mg/g) 175 0.35 Linolenic acid (˜4 mg/g) 335 1.34 Carbohydrates Cellulose (˜100 mg/g) 970 60 Hemicellulose (˜100 mg/g) 976 60 Pectin (˜100 mg/g) 100 10 Glucose (˜140 mg/g) 786 98 Polyphenols Lignin (˜40 mg/g) 934 18 Chlorogenic acid (˜8 mg/g) ND ND = not detected. ^(a)= B[a]P yield normalized to the amount of the component present in tobacco ^(b)= approximate amounts reported to be present in bright tobacco

A carbohydrate+lignin mixture (Carbo-Lig mix) was pryolyzed in the presence of an amino acid (proline) and a mixture of tobacco lipid components. 0.4% w/w of D(+)-proline was physically mixed with the Carbo-Lig mix. The lipid mixture consisted of oleic acid (1 mg/g), linoleic acid (2 mg/g), linolenic acid (3.5 mg/g), stigmasterol (0.8 mg/g), chlorogenic acid (8 mg/g) and solanesol (15 mg/g). The amounts of amino acid and lipids added are consistent with the amount of each component present in bright tobacco. As shown in FIG. 2, neither the addition of an amino acid (at 0.4% w/w) nor doubling the concentration of lipids (oleic acid, linoleic acid, linolenic acid, stigmasterol, chlorogenic acid, and solanesol) significantly affected the yield of B[a]P formed from the Carbo-Lig mix.

Extraction of bright tobacco lamina with hexane and ethyl acetate removes lipophilic components of tobacco but does not lead to a decrease in B[a]P formed. Extraction with methanol decreases the B[a]P yield by 35% whereas extraction with water significantly increases the yield of B[a]P. The methanol extraction process appears to remove low temperature B[a]P precursors while extraction with water appears to concentrate B[a]P precursors on a per gram of material basis. From the individual tobacco components pyrolyzed at 600° C., only the tobacco carbohydrates and cell wall components such as glucose, cellulose, hemicellulose and lignin appear to contribute significantly to the formation of B[a]P. Extraction of tobacco (such as flue cured tobacco) with ethanol, 1-propanol or 2-propanol can also reduce generation of B[a]P during smoking. The extraction with the methanol, ethanol, 1-propanol or 2-propanol is preferably carried out on tobacco which has not been subjected to a prior extraction with acetone. The extraction is preferably carried out using a single solvent selected from the group consisting of methanol, ethanol, 1-propanol and 2-propanol.

While various embodiments have been described, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the claims appended hereto. 

1. A process for manufacturing a smoking article having reduced generation of benzo[a]pyrene during smoking thereof comprising preparing a treated tobacco by contacting a tobacco material with an extraction solvent consisting essentially of a solvent selected from the group consisting of methanol, ethanol, 1-propanol and 2-propanol, the extraction being carried out on tobacco which has not been subjected to extraction with acetone; and incorporating the treated tobacco in a smoking article.
 2. The process according to claim 1 wherein the tobacco material comprises bright, burley, oriental and other tobacco lamina.
 3. The process according to claim 1 wherein the tobacco material comprises flue cured tobacco lamina.
 4. The process according to claim 1 wherein the contacting is carried out in a Soxhlet extractor.
 5. The process according to claim 1 wherein the contacting results in a reduction in weight of the tobacco material.
 6. The process according to claim 5 wherein the reduction is at least about 25%.
 7. The process according to claim 5 wherein the reduction is at least about 40%.
 8. The process according to claim 1 wherein the smoking article exhibits a reduction in benzo[a]pyrene in tobacco smoke of at least about 25% when the treated tobacco is pyrolyzed at 600° C. in an inert atmosphere.
 9. The process according to claim 1 wherein the smoking article is a cigarette.
 10. The process according to claim 1 wherein the contacting removes benzo[a]pyrene precursors.
 11. A smoking article comprising the treated tobacco produced according to the process of claim
 1. 12. A cigarette comprising the treated tobacco produced according to the process of claim
 1. 13. The smoking article of claim 11 wherein the smoking article exhibits a reduction in benzo[a]pyrene in tobacco smoke of at least about 25% when the treated tobacco is pyrolyzed at 600° C. in an inert atmosphere.
 14. The cigarette of claim 12 wherein the cigarette exhibits a reduction in benzo[a]pyrene in tobacco smoke of at least about 25% when the treated tobacco is pyrolyzed at 600° C. in an inert atmosphere.
 15. The smoking article of claim 11 wherein the smoking article exhibits a reduction in benzo[a]pyrene in tobacco smoke of at least about 35% when the treated tobacco is pyrolyzed at 600° C. in an inert atmosphere.
 16. The cigarette of claim 12 wherein the cigarette exhibits a reduction in benzo[a]pyrene in tobacco smoke of at least about 35% when the treated tobacco is pyrolyzed at 600° C. in an inert atmosphere.
 17. The process according to claim 1, wherein the extraction is carried out with a solvent consisting of methanol.
 18. The process according to claim 1, wherein the extraction is carried out with a solvent consisting of ethanol.
 19. The process according to claim 1, wherein the extraction is carried out with a solvent consisting of 1-propanol.
 20. The process according to claim 1, wherein the extraction is carried out with a solvent consisting of 2-propanol.
 21. A process for producing tobacco having reduced generation of benzo[a]pyrene during smoking thereof comprising preparing a treated tobacco by contacting a tobacco material with an extraction solvent consisting essentially of a solvent selected from the group consisting of methanol, ethanol, 1-propanol and 2-propanol, wherein the tobacco is not subjected to extraction with acetone. 